[PATCH 5.4] firmware: arm_scmi: Fix device node validation for mailbox transport

[Cristian Marussi <cristian.marussi@arm.com>]

commit 2ab4f4018cb6b8010ca5002c3bdc37783b5d28c2 upstream.

When mailboxes are used as a transport it is possible to setup the SCMI
transport layer, depending on the underlying channels configuration, to use
one or two mailboxes, associated, respectively, to one or two, distinct,
shared memory areas: any other combination should be treated as invalid.

Add more strict checking of SCMI mailbox transport device node descriptors.

Fixes: fbc4d81ad285 ("firmware: arm_scmi: refactor in preparation to support per-protocol channels")
Cc: <stable@vger.kernel.org> # 5.4
Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
Link: https://lore.kernel.org/r/20230307162324.891866-1-cristian.marussi@arm.com
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
[Cristian: backported to v5.4]
Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
---
Backporting just trivially adapting to v5.4 context.
---
 drivers/firmware/arm_scmi/driver.c | 37 ++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/drivers/firmware/arm_scmi/driver.c b/drivers/firmware/arm_scmi/driver.c
index f0b055bc027c..9dae841b6167 100644
--- a/drivers/firmware/arm_scmi/driver.c
+++ b/drivers/firmware/arm_scmi/driver.c
@@ -737,6 +737,39 @@ static int scmi_mailbox_check(struct device_node *np, int idx)
 					  idx, NULL);
 }
 
+static int scmi_mailbox_chan_validate(struct device *cdev)
+{
+	int num_mb, num_sh, ret = 0;
+	struct device_node *np = cdev->of_node;
+
+	num_mb = of_count_phandle_with_args(np, "mboxes", "#mbox-cells");
+	num_sh = of_count_phandle_with_args(np, "shmem", NULL);
+	/* Bail out if mboxes and shmem descriptors are inconsistent */
+	if (num_mb <= 0 || num_sh > 2 || num_mb != num_sh) {
+		dev_warn(cdev, "Invalid channel descriptor for '%s'\n",
+			 of_node_full_name(np));
+		return -EINVAL;
+	}
+
+	if (num_sh > 1) {
+		struct device_node *np_tx, *np_rx;
+
+		np_tx = of_parse_phandle(np, "shmem", 0);
+		np_rx = of_parse_phandle(np, "shmem", 1);
+		/* SCMI Tx and Rx shared mem areas have to be distinct */
+		if (!np_tx || !np_rx || np_tx == np_rx) {
+			dev_warn(cdev, "Invalid shmem descriptor for '%s'\n",
+				 of_node_full_name(np));
+			ret = -EINVAL;
+		}
+
+		of_node_put(np_tx);
+		of_node_put(np_rx);
+	}
+
+	return ret;
+}
+
 static int scmi_mbox_chan_setup(struct scmi_info *info, struct device *dev,
 				int prot_id, bool tx)
 {
@@ -760,6 +793,10 @@ static int scmi_mbox_chan_setup(struct scmi_info *info, struct device *dev,
 		goto idr_alloc;
 	}
 
+	ret = scmi_mailbox_chan_validate(dev);
+	if (ret)
+		return ret;
+
 	cinfo = devm_kzalloc(info->dev, sizeof(*cinfo), GFP_KERNEL);
 	if (!cinfo)
 		return -ENOMEM;
-- 
2.34.1